Display apparatus and method of operating the same

ABSTRACT

A display apparatus may include a first substrate defined by a pixel region and a transmitting region adjacent to the pixel region, the pixel region emitting light in a first direction and the transmitting region transmitting external light; a second substrate that faces the first substrate and seals pixels defined on the first substrate; an optical filter arranged on a first side of the display apparatus through which light is emitted, the optical filter being configured to transmit circularly polarized light that rotates in a predetermined direction; and an optical reflectance conversion device arranged on a second side of the display apparatus, opposite the first side, the optical reflectance conversion device being configured to change a reflectance of the external light according to modes of operation of the display apparatus.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This is a continuation application based on pending application Ser. No.13/137,958, filed Sep. 22, 2011, the entire contents of which is herebyincorporated by reference.

This application claims the benefit of Korean Patent Application No.10-2011-0038440, filed on Apr. 25, 2011, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

Embodiments relate to a display apparatus. More particularly,embodiments relate to a display apparatus that can change opticaltransmittance according to modes, and a method of operating the same.

2. Description of the Related Art

Applications of organic light-emitting display apparatuses haveincreased from personal portable devices, i.e., MP3 players or mobilephones, to television sets due to wide viewing angles, high contrast,short response times, and low power consumption. Organic light-emittingdisplay apparatuses have an emissive characteristic. Thus, unlike aliquid crystal display apparatus, organic light-emitting displayapparatuses do not require an additional light source. Accordingly, thethickness and weight of organic light-emitting devices may be reduced.Also, the organic light-emitting display apparatuses may be formed intransparent display apparatuses by forming thin-film transistors andorganic light-emitting devices therein of a transparent type, and byforming a transparent region (or transparent window) separate from apixel region.

SUMMARY

According to an embodiment, a display apparatus may include a firstsubstrate defined by a pixel region and a transmitting region adjacentto the pixel region, the pixel region emitting light in a firstdirection and the transmitting region transmitting external light; asecond substrate that faces the first substrate and seals pixels definedon the first substrate; an optical filter arranged on a first side ofthe display apparatus through which light is emitted, the optical filterbeing configured to transmit circularly polarized light that rotates ina predetermined direction; and an optical reflectance conversion devicearranged on a second side of the display apparatus, opposite the firstside, the optical reflectance conversion device being configured tochange a reflectance of the external light according to modes ofoperation of the display apparatus.

The pixel may include a pixel circuit unit in the pixel region on thefirst substrate, the pixel circuit unit including at least one thin-filmtransistor; a first insulating film covers at least the pixel circuitunit; a first electrode on the first insulating film electricallyconnected to the pixel circuit unit, the first electrode located in thepixel region and not overlapping the pixel circuit unit, and the firstelectrode is formed of a transparent conductive material; a secondelectrode configured to reflect light to be emitted in a directiontowards the first electrode, the second electrode facing the firstelectrode and located in the pixel region; and an organic film betweenthe first electrode and the second electrode and includes alight-emitting layer.

The optical filter may be on an outer side of the first substrate andthe optical reflectance conversion device may be on an outer side of thesecond substrate.

The pixel may include the transmitting region and a plurality of thepixel regions separated from each other by interposing the transmittingregion therebetween.

The display apparatus may further include a second insulating film thatdoes not cover some of the first electrode, the second insulating filmlocated at least on a pixel region portion of the pixel region and onthe transmitting region on the first insulating film, wherein theorganic film is located on a first electrode portion of the firstelectrode that is not covered by the second insulating film.

The pixel may include a pixel circuit unit located in the pixel regionon the first substrate, the pixel circuit unit including at least onethin-film transistor; a first insulating film to cover at least thepixel circuit unit; a first electrode on the first insulating film andelectrically connected to the pixel circuit unit, the first electrodelocated in the pixel region and overlapping with the pixel circuit unit,and the first electrode includes a conductive material reflection film;a second electrode facing the first electrode and configured to reflectlight to be emitted in a direction opposite to the first electrode; andan organic film between the first electrode and the second electrode,the organic film including a light-emitting layer.

The optical filter may be on an outer side of the second substrate andthe optical reflectance conversion device may be on an outer side of thefirst substrate.

The pixel may include the transmitting region and the plurality of thepixel regions separated from each other by interposing the transmittingregion.

The display apparatus may further include a second insulating film thatdoes not cover some of the first electrode, the second insulating filmlocated at least on a portion of the pixel region and on thetransmitting region on the first insulating film, wherein the organicfilm is located on a firs electrode portion of the first electrode thatis not covered by the second insulating film.

The optical filter may be a combination of a linear polarizing filterand a Lamda/4 retarder or a circularly polarizing filter.

The optical reflectance conversion device may have a limitation that asum of the reflectance of the external light and the transmittance ofthe external light is one.

The optical reflectance conversion device may be a liquid crystal deviceor an electro-chromic device.

The electro-chromic device may include: a pair of transparent electrodelayers to which power is applied; and an electro-chromic material layerbetween the transparent electrode layers and including anelectro-chromic material, a phase of which is changed by a power appliedto the transparent electrode layers to control the optical reflectanceof the display apparatus.

In a first mode, the optical reflectance conversion device may transmitthe external light that enters through the optical filter and thedisplay device.

In a second mode, the optical reflectance conversion device may reflectthe external light entering through the optical filter and the displaydevice.

In the second mode, the external light that is reflected by the opticalreflectance conversion device may not be re-transmitted through theoptical filter.

In a third mode, the optical reflectance conversion device may reflectan external light portion of the external light entering through theoptical filter and the display device and transmits the other externallight portion of the external light.

In the third mode, the external light portion of the external light thatis reflected by the optical reflectance conversion device may not bere-transmitted through the optical filter.

According to another embodiment, a method of operating the displayapparatus may include a display, an optical filter arranged on a firstside of the display apparatus to which light is emitted, the opticalfilter being configured to transmit circularly polarized light thatrotates in a predetermined direction; and an optical reflectanceconversion device arranged on a second side of the display apparatus,opposite the first side, the optical reflectance conversion device beingconfigured to change a reflectance of the external light according tomodes of operation of the display apparatus, the method includingrealizing a first mode, a second mode, and a third mode by controllingthe reflectance of the external light that is transmitted through theoptical filter and the display device by applying different powers tothe optical reflectance conversion device.

Realizing the first mode may include: applying a first power to theoptical reflectance conversion device; displaying an image in the firstdirection in the display device; and transmitting the external light ina second direction, opposite the first direction, through the opticalfilter, the display device, and the optical reflectance conversiondevice.

Realizing the second mode may include: applying a second power to theoptical reflectance conversion device; displaying an image in the firstdirection in the display device; transmitting the external light in asecond direction, opposite the first direction, through the opticalfilter and the display device; reflecting the external light transmittedthrough the optical filter and the display device in the first directionby the optical reflectance conversion device; and transmitting reflectedexternal light through the display device, but not through the opticalfilter.

Realizing the third mode may include: applying a third power to theoptical reflectance conversion device; displaying an image in the firstdirection in the display device; transmitting the external light in asecond direction, opposite the first direction, through the opticalfilter and the display device; reflecting a first portion of theexternal light transmitted through the optical filter and the displaydevice in the first direction by the optical reflectance conversiondevice and transmitting a second portion of the external light in thesecond direction through the optical reflectance conversion device; andtransmitting reflected external light through the display device, butnot through the optical filter.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features will become more apparent by describing indetail exemplary embodiments thereof with reference to the attacheddrawings in which:

FIG. 1 is a schematic cross-sectional view of a display apparatusaccording to an embodiment;

FIG. 2 is a plan view showing a pixel included in the display device ofFIG. 1, according to an embodiment;

FIG. 3 is a plan view showing a pixel included in the display device ofFIG. 1, according to another embodiment;

FIG. 4 is a cross-sectional view of one of a plurality of sub-pixelsdepicted in FIGS. 2 and 3, according to an embodiment;

FIG. 5 is a schematic cross-sectional view of a display apparatusaccording to another embodiment;

FIG. 6 is a plan view showing a pixel included in the display device ofFIG. 5, according to another embodiment;

FIG. 7 is a plan view showing a pixel included in the display device ofFIG. 5, according to another embodiment;

FIG. 8 is a cross-sectional view of one of a plurality of sub-pixelsdepicted in FIGS. 6 and 7, according to another embodiment;

FIGS. 9 through 11 are schematic drawings showing methods of operatingin each mode of a display apparatus according to an embodiment; and

FIG. 12 is a schematic drawing showing an optical reflectance conversiondevice included in a display apparatus, according to an embodiment.

DETAILED DESCRIPTION

Example embodiments will now be described more fully hereinafter withreference to the accompanying drawings; however, they may be embodied indifferent forms and should not be construed as limited to theembodiments set forth herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an,” and “the,”are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “comprises,” “comprising,” “includes,” and/or “including,” whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Present embodiments will now be described more fully with reference tothe accompanying drawings in which exemplary embodiments are shown.Throughout the drawings, like reference numerals have been used todesignate like elements.

FIG. 1 is a schematic cross-sectional view of a display apparatus 100according to an embodiment.

Referring to FIG. 1, the display apparatus 100 includes an opticalfilter 3 and an optical reflectance conversion device 4 on a transparentdisplay device 10 through which external light may be transmitted.

The display device 10 may be a bottom emission type organiclight-emitting display device and may include a first substrate 1, adisplay unit formed on the first substrate 1, and a second substrate 2that seals the display unit. The display unit may be defined to aplurality of pixels, and the pixels may include a pixel region 31through which light is emitted in a direction towards the firstsubstrate 1, and a transmitting region 32 that is adjacent to the pixelregion 31 to transmit external light.

The optical filter 3 is disposed on an outer side of the first substrate1 through which the display device 10 emits light. An aspect of theoptical filter 3 is that the optical filter 3 allows circularlypolarized light that rotates in a predetermined direction to transmittherethrough. Accordingly, the optical filter 3 may be a combination ofa linearly polarizing light filter and a Lamda/4 retarder which is aphase change device or a circularly polarizing light filter.

The optical reflectance conversion device 4 is disposed on an outer sideof the second substrate 2 through which the display device 10 does notemit light. The optical reflectance conversion device 4 changes thereflectance of external light according to modes. The opticalreflectance conversion device 4 may be a liquid crystal device that canchange optical transmittance or reflectance by changing the arrangementof liquid crystals according to an application of an electric field oran electro-chromic device that can change optical transmittance orreflectance by changing the state of an electro-chromic materialaccording to an application of power.

The optical reflectance conversion device 4 has a limitation that thesum of reflectance and transmittance always satisfy 1 (or 100%). Acontrast ratio of the display apparatus 100 is expressed as thefollowing equation 1, and the contrast ratio of the display apparatus100 may be simply controlled by using the optical reflectance conversiondevice 4. If there is no limitation described above, the contrast ratioof the display apparatus 100 must be controlled by using the twovariables, that is, reflectance and transmittance. However, since theoptical reflectance conversion device 4 has the limitation as describedabove, the contrast ratio of the display apparatus 100 may be simplycontrolled by controlling one of the reflectance and transmittance.

$\begin{matrix}{{{contrast}\mspace{14mu} {ratio}} \propto \frac{1}{{reflectance} \times \left( {1 - {transmittance}} \right)}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

According to the current embodiment, when the optical reflectanceconversion device 4 is in an optical transmitting mode, a user who ispositioned on a side where an image is realized may view an imagedisplayed on the outer side of the second substrate 2 through a firstexternal light transmitted towards the outer side of the first substrate1. Also, a second external light may not effect on the contrast ratio ofthe display apparatus 100 since the second external light is transmittedthrough the display apparatus 100. Here, the first external light istransmitted in the same direction as the image, and the second externallight is transmitted in a direction opposite to the first externallight.

When the optical reflectance conversion device 4 is in an opticalreflection mode, the first external light may not be transmitted throughthe display apparatus 100. However, in this mode, the second externallight that is transmitted towards the outer side of the second substrate2 from the outer side of the first substrate 1 is reflected by theoptical reflectance conversion device 4, and thus, is transmittedtowards the outer side of the first substrate 1, thereby reducing thecontrast ratio of the display apparatus 100. According to the currentembodiment, in order to address the above problem, the reduction of thecontrast ratio of the display apparatus 100 is prevented by disposingthe optical filter 3. The operation of the display apparatus 100according to present embodiments will be described in detail below withreference to FIGS. 9 through 11.

FIG. 2 is a plan view showing a pixel included in the display device 10of FIG. 1, according to an embodiment. FIG. 3 is a plan view showinganother example of a pixel included in the display device 10 of FIG. 1,according to another embodiment.

A pixel may include a plurality of sub-pixels, for example, red, green,and blue sub-pixels Pr, Pg, and Pb.

Each of the red, green, and blue sub-pixels Pr, Pg, and Pb includes thepixel region 31 and the transmitting region 32. Each of the pixelregions 31 includes a pixel circuit unit 311 and a light-emitting unit312, wherein the pixel circuit unit 311 and the light-emitting unit 312are disposed to adjacent to each other not to overlap. This is becausewhen the light-emitting unit 312 emits light towards the first substrate1, i.e., a bottom emission type display apparatus, the light path maynot be interrupted by the pixel circuit unit 311.

The transmitting region 32 that transmits external light is disposedadjacent to the pixel region 31.

As shown in FIG. 2, each of the transmitting regions 32 is independentlyformed in the red, green, and blue sub-pixels Pr, Pg, and Pb. As shownin FIG. 3, each of the transmitting regions 32 may be connected to eachother throughout the red, green, and blue sub-pixels Pr, Pg, and Pb. Inother words, taking the display unit as a whole, a pixel may include aplurality of pixel regions 31 separated from each other interposingcommon transmitting regions 32 therebetween. In the case of thetransmitting region 32 of FIG. 3, there is an effect of increasing anarea of the transmitting region 32, and thus, the overall transmittanceof the display unit may be increased.

In FIG. 3, the red, green, and blue sub-pixels Pr, Pg, and Pb in thetransmitting region 32 are depicted as connected to each other. However,present embodiments are not limited thereto, and the transmittingregions 32 of any two of the red, green, and blue sub-pixels Pr, Pg, andPb may be connected to each other.

FIG. 4 is a cross-sectional view of one of the red, green, and bluesub-pixels Pr, Pg, and Pb depicted in FIGS. 2 and 3.

Referring to FIG. 4, a thin-film transistor TR is disposed in the pixelcircuit unit 311. However, the pixel circuit unit 311 may notnecessarily include one thin-film transistor TR but may include a pixelcircuit that includes the thin-film transistor TR. The pixel circuit mayfurther include a plurality of thin-film transistors and storagecapacitors, and may further include a scan line, a data line, and a Vddline connected to the thin-film transistors and the storage capacitors.

An organic light-emitting device EL, which is a light-emitting device,is disposed in the light-emitting unit 312. The organic light-emittingdevice EL is electrically connected to the thin-film transistor TR ofthe pixel circuit unit 311.

First, a buffer film 211 is formed on the first substrate 1, and a pixelcircuit having a thin-film transistor TR is formed on the buffer film211.

A semiconductor active layer 212 is formed on the buffer film 211.

The buffer film 211 prevents the penetration of impurity elements andplanarizes a surface. The buffer film 211 may be formed of variousmaterials, for example, an inorganic material selected from the groupconsisting of silicon oxide, silicon nitride, silicon oxynitride,aluminium oxide, aluminium nitride, titanium oxide, and titanium nitrideor an organic material selected from the group consisting of polyimide,polyester, and acryl, or stack layers of these materials. The bufferfilm 211 is not an essential constituent element, and thus, may not beincluded if it is unnecessary.

The semiconductor active layer 212 may be formed of polycrystal siliconbut is not limited thereto. The semiconductor active layer 212 may beformed of an oxide semiconductor oxide, i.e., a [(In₂O₃)a(Ga₂O₃)b(ZnO)c](G-I-Z-O) layer (where a, b, and c are real numbers that respectivelysatisfy a≧0, b≧0, c>0). When the semiconductor active layer 212 isformed of an oxide semiconductor, optical transmittance of the pixelcircuit unit 311 in the pixel region 31 may be increased. Accordingly,the external light transmittance of the entire display unit may beincreased.

A gate insulating film 213, covering the semiconductor active layer 212,is formed on the buffer film 211, and a gate electrode 214 is formed onthe gate insulating film 213.

An interlayer insulating film 215, covering the gate electrode 214, isformed on the gate insulating film 213, and a source electrode 216 and adrain electrode 217 are formed on the interlayer insulating film 215.The source electrode 216 and the drain electrode 217 are connected tothe semiconductor active layer 212 through contact holes, respectively.

The structure of the thin-film transistor TR is not limited thereto.That is, the thin-film transistor TR may have various types ofstructures.

A passivation film 218 is formed to cover the thin-film transistor TR.The passivation film 218 may be a single layer or a multi-layerinsulating film having an upper surface thereof that is planarized. Thepassivation film 218 may be formed of an inorganic material or organicmaterial. The passivation film 218 is formed to cover both of the pixelregion 31 and the transmitting region 32.

As shown in FIG. 4, a first electrode 221 of the organic light-emittingdevice EL electrically connected to the thin-film transistor TR isformed on the passivation film 218. The first electrode 221 is formed asan island type electrode independently in each of the red, green, andblue sub-pixels Pr, Pg, and Pb. The first electrode 221 is positioned inthe light-emitting unit 312 of the pixel region 31, and is disposed notto overlap the pixel circuit unit 311.

A pixel-defining film 219 is formed on the passivation film 218 using anorganic and/or inorganic insulating material.

The pixel-defining film 219 includes a first opening 219 a to coveredges and to expose a central region of the first electrode 221. At thispoint, the pixel-defining film 219 may be formed to cover the pixelregion 31. However, the pixel-defining film 219 may not necessarilycover the whole pixel region 31, but may cover at least a portion of thepixel region 31, i.e., edges of the first electrode 221. Thepixel-defining film 219 is disposed not in the transmitting region 32.Since the pixel-defining film 219 is not disposed in the transmittingregion 32, the optical transmission efficiency of external light in thetransmitting region 32 may further be increased.

An organic film 223 and a second electrode 222 are sequentially formedon the first electrode 221 exposed through the first opening 219 a. Thesecond electrode 222 faces the first electrode 221, covers the organicfilm 223 and the pixel-defining film 219, and is located in the pixelregion 31. The second electrode 222 is not disposed in the transmittingregion 32.

The organic film 223 may be a low molecular weight organic film or apolymer organic film. When the organic film 233 is a low molecularweight organic film, the organic film 223 may be formed in a singlelayer or a composite layer structure by stacking a hole injection layer(HIL), a hole transport layer (HTL), an emission layer (EML), anelectron transport layer (ETL), an electron injection layer (EIL) andmay be formed of various materials including copper phthalocyanine(CuPc), N,N′-Di(naphthalene-1-yl)-N,N-diphenyl-benzidine (NPB), ortris-8-hydroxyquinoline aluminum (Alq3). The low molecular weightorganic film may be formed by using an evaporation method. At thispoint, the HIL, the HTL, the ETL, and the EIL are common layers, andthus, may be commonly applied to the red, green, and blue sub-pixels Pr,Pg, and Pb.

The first electrode 221 may perform as an anode electrode, and thesecond electrode 222 may performed as a cathode electrode. However, thepolarities of the first electrode 221 and the second electrode 222 maybe reversed.

According to the current embodiment, the first electrode 221 may be atransparent electrode, and the second electrode 222 may be a reflectionelectrode. The first electrode 221 may be formed of a transparentconductive material, i.e., a material of ITO, IZO, ZnO, and In₂O₃. Thesecond electrode 222 may be formed of a metal of Ag, Mg, Al, Pt, Pd, Au,Ni, Nd, Ir, Cr, Li, and Ca. Accordingly, the organic light-emittingdevice EL is a bottom emission type organic light-emitting device thatproduces an image in a direction towards the first electrode 221. Inthis case, the second electrode 222 may be formed to have a thicknesssufficient enough to prevent an entire voltage drop of the display unit,and thus, may be sufficient to be applied to a large-area displayapparatus 100.

FIG. 5 is a schematic cross-sectional view of a display apparatus 100according to another embodiment.

The display apparatus 100 in FIG. 5, unlike in the display apparatus 100of FIG. 1, may be a top emission type organic light-emitting device inwhich the display device 10 is a top emission type device. Accordingly,the optical filter 3 is disposed on an outer side of the secondsubstrate 2 through which the display device 10 emits light. The opticalreflectance conversion device 4 is disposed on an outer side of thefirst substrate 1 through which the display device 10 does not emitlight. The rest of the constituent elements of FIG. 5 correspond to theconstituent elements of FIG. 1 and have substantially the same orsimilar functions to the constituent elements described in the previousembodiment of FIG. 1. Thus, the description thereof will not berepeated.

As depicted in FIG. 5, according to the current embodiment, when theoptical reflectance conversion device 4 is in an optical transmittingmode, a user at a side where an image is realized may view the imagedisplayed on the outer side of the first substrate 1 from a firstexternal light that is transmitted in a direction towards the outer sideof the second substrate 2. Also, the second external light does noteffect the contrast ratio since the second external light is transmittedthrough the display apparatus 100.

When the optical reflectance conversion device 4 is in an opticalreflection mode, the first external light may not be transmitted throughthe display apparatus 100. However, in this mode, there is a problem inthat the second external light transmitted towards the outer side of thefirst substrate 1 from the outer side of the second substrate 2 isreflected by the optical reflectance conversion device 4, and thus, isemitted towards the outer side of the second substrate 2, therebyreducing the contrast ratio of the display apparatus 100. It is anaspect of the current embodiment that, in order to address the aboveproblem, the optical filter 3 is disposed to reduce the reduction of thecontrast ratio. The operation of the display apparatus 100 according tothe current embodiment will be described in detail below with referenceto FIGS. 9 through 11.

FIG. 6 is a plan view showing a pixel included in the display device 10of FIG. 5, according to another embodiment . FIG. 7 is a plan viewshowing a pixel included in the display device 10 of FIG. 5, accordingto another embodiment.

In the pixels depicted in FIGS. 6 and 7, unlike the pixels in FIGS. 2and 3, the pixel circuit unit 311 and the light-emitting unit 312included in the pixel region 31 overlap with each other. Since thelight-emitting unit 312 emits light in a direction towards the secondsubstrate 2, that is, the light-emitting unit 312 is a top emission typedisplay apparatus, the overlapping of the pixel circuit unit 311 and thelight-emitting unit 312 may not affect the contrast ratio of the displayapparatus 100. In addition, since the light-emitting unit 312 covers thepixel circuit unit 311 that includes a pixel circuit, opticalinterference by pixel circuit may be avoided. The rest of theconstituent elements of FIGS. 6 and 7 correspond to the constituentelements of FIGS. 2 and 3 and have substantially the same or similarfunctions to the constituent elements described in the previousembodiments of FIGS. 2 and 3. Thus, the description thereof will not berepeated.

As shown in FIG. 6, each of the transmitting regions 32 may beindependently formed in the red, green, and blue sub-pixels Pr, Pg, andPb. Also, as shown in FIG. 7, may be connected to each other across thered, green, and blue sub-pixels Pr, Pg, and Pb.

FIG. 8 is a cross-sectional view of one of the red, green, and bluesub-pixels Pr, Pg, and Pb depicted in FIGS. 6 and 7, according toanother embodiment.

Referring to FIG. 8, a thin-film transistor TR is disposed in the pixelcircuit unit 311 and an organic light-emitting device EL, which is alight-emitting device, is disposed in the light-emitting unit 312.

The buffer film 211 is formed on the first substrate 1, a semiconductoractive layer 212 is formed on the buffer film 211, and the gateinsulating film 213, the gate electrode 214, and the interlayerinsulating film 215 are formed on the semiconductor active layer 212.The source electrode 216 and the drain electrode 217 are formed on theinterlayer insulating film 215. A passivation film 218, which is a kindof insulating film, is formed to cover the thin-film transistor TR. Thepassivation film 218 covers both the pixel region 31 and thetransmitting region 32.

As shown in FIG. 8, the first electrode 221 of the organiclight-emitting device EL that is electrically connected to the thin-filmtransistor TR is formed on the passivation film 218. The first electrode221 is disposed in the light-emitting unit 312 of the pixel region 31,and covers the pixel circuit unit 311 by overlapping with the pixelcircuit unit 311.

The pixel-defining film 219 is formed on the passivation film 218 usingan organic and/or inorganic insulating material.

The pixel-defining film 219 includes the first opening 219 a to coveredges of the first electrode 221 and to expose a central region of thefirst electrode 221. At this point, the pixel-defining film 219 may beformed to cover the pixel region 31. However, the pixel-defining film219 may not necessarily cover the whole pixel region 31, but may coverat least a portion of the pixel region 31, i.e., the edges of the firstelectrode 221. The pixel-defining film 219 is disposed not in thetransmitting region 32. Since the pixel-defining film 219 is notdisposed in the transmitting region 32, the optical transmissionefficiency of external light in the transmitting region 32 may beincreased.

The organic film 223 and the second electrode 222 are sequentiallystacked on the first electrode 221 exposed through the first opening 219a.

According to the current embodiment, in the sub-pixel depicted in FIG.8, the first electrode 221 may be formed in a stack structure of atransparent conductor and a reflection film, and the second electrode222 may be a semi-reflection and semi-transmission electrode. Here, thetransparent conductor may be formed of a material having a high workfunction, for example, may be one of ITO, IZO, ZnO, and In₂O₃. Thereflection film may be formed of at least one metal of Ag, Mg, Al, Pt,Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Mo, and an alloy of these metals. Thefirst electrode 221 is formed in the pixel region 31.

The second electrode 222 may be formed of one metal of Ag, Mg, Al, Pt,Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, Mo, and an alloy of these metals. Thesecond electrode 222 may be formed as a thin film having a thickness ina range from about 100 Å(angstrom) to 300 Å(angstrom) to have a hightransmittance. Accordingly, the organic light-emitting device EL is atop emission type organic light-emitting device that produces an imagein a direction towards the second electrode 222.

FIGS. 9 through 11 are schematic drawings showing methods of operatingin each mode of the display apparatus 100 according to an embodiment.

The display apparatus 100 operates in three modes. Each of the modes isdistinguished according to the optical reflectance of the opticalreflectance conversion device 4, and the optical reflectance isdetermined according to a power applied to the optical reflectanceconversion device 4.

Referring to FIG. 9, the first mode is a case when the opticalreflectance conversion device 4 transmits all light. In the first mode,a first power is applied to the optical reflectance conversion device 4.

An image 50 is emitted in a D1 direction in the display device 10. Atthis point, a user located in a direction in which the image 50 isemitted may view an object located on an outer side of the opticalreflectance conversion device 4 due to the first external light 51 thathas transmitted through the display apparatus 100 in the D1 direction.

The second external light 52 may be transmitted in a D2 directionthrough the optical filter 3, the display device 10, and the transparentoptical reflectance conversion device 4. However, the second externallight 52′ that is transmitted through the optical filter 3 becomes acircularly polarized light that rotates in a predetermined direction.

FIG. 10 shows a second mode in which the optical reflectance conversiondevice 4 does not transmit but reflects light. In the second mode, asecond power different from the first power is applied to the opticalreflectance conversion device 4.

The image 50 is emitted in the D1 direction in the display device 10. Atthis point, the user located in the direction in which the image isemitted may not view an object located on the outer side of the opticalreflectance conversion device 4. This is because the first externallight 51 is not transmitted in the D1 direction through the displayapparatus 100 since the optical reflectance conversion device 4 reflectsall light.

Meanwhile, the second external light may be transmitted through theoptical filter 3 and the display device 10 in the D2 direction. Also,the second external light 52′ that is transmitted through the opticalfilter 3 becomes a circularly polarized light that rotates in apredetermined direction. Also, all of the second external light 52′ isreflected in the D1 direction by the optical reflectance conversiondevice 4 and becomes a second external light 52″. In this way, thesecond external light 52″ reflected by the optical reflectanceconversion device 4 has a converted rotational direction, and thus,becomes a circularly polarized light that rotates in a directiondifferent from the second external light 52′. Accordingly, the secondexternal light 52″ may be transmitted through the transparent displaydevice 10 but may not be transmitted through the optical filter 3.

According to the current embodiment, since the second external light 52″that is reflected by the optical reflectance conversion device 4 may notbe transmitted through the optical filter 3, the second external light52″ may not reach the user located on a side where the image 50 isemitted. Accordingly, the external light reflection is removed, andthus, a maximum contrast ratio of the display apparatus 100 is realized.When the display apparatus 100 described above is used, a black colormay be clearly realized in a bright environment without the reflectionof external light.

FIG. 11 shows a third mode in which the optical reflectance conversiondevice 4 transmits a portion of light, and simultaneously, reflects theremaining portion of light. Here, the optical reflectance conversiondevice 4 has a limitation that the sum of reflectance and transmittanceis 1. In the third mode, a third power different from the first andsecond powers is applied to the optical reflectance conversion device 4.

The image 50 is emitted in the D1 direction in the display device 10. Atthis point, the user located in the direction in which the image 50 isemitted may view to some degree an object located on the outer side ofthe optical reflectance conversion device 4. This is because the opticalreflectance conversion device 4 transmits a portion of the firstexternal light 51 and reflects the remaining portion of light. A firstexternal light 51′ that has transmitted through the optical reflectanceconversion device 4 reaches the user by progressing in the D1 directionthrough the display device 10 and the optical filter 3. The firstexternal light 51″ is reflected by the optical reflectance conversiondevice 4, and the sum of the reflectance and the transmittance of theoptical reflectance conversion device 4 must be 1 (or 100%).

The second external light 52 may be transmitted through the opticalfilter 3 and the display device 10 in the D2 direction. The secondexternal light 52′ that is transmitted through the optical filter 3becomes a circularly polarized light that rotates in a predetermineddirection. A portion of the second external light 52′ is reflected inthe D1 direction by the optical reflectance conversion device 4 andbecomes a second external light 52″. The remaining portion of the secondexternal light 52′ becomes a second external light 52″′ that hastransmitted through the optical reflectance conversion device 4 in theD2 direction. Here, since the sum of the reflectance and transmittanceof the optical reflectance conversion device 4 is 1 (or 100%), when thesecond external light 52″ and the second external light 52″′ are added,the sum may be the second external light 52′. Here, the second externallight 52″ reflected by the optical reflectance conversion device 4 has aconverted rotational direction, and thus, is a circularly polarizedlight that rotates in a direction different from that of the secondexternal light 52′. Accordingly, the second external light 52″ may betransmitted through the display device 10 but may not be transmittedthrough the optical filter 3. For reference, the second external light52″′ that has transmitted through the optical reflectance conversiondevice 4 is a circularly polarized light that rotates in the samedirection as the second external light 52′.

According to the current embodiment, since the second external light 52″that is reflected by the optical reflectance conversion device 4 cannotbe transmitted through the optical filter 3, the second external light52″ may not reach the user located in a direction in which the image isemitted. Accordingly, the external light reflection is removed in thethird mode in which the optical reflectance conversion device 4 is asemi-transparent, and thus, the contrast ratio of the display apparatus100 is not reduced.

FIG. 12 is a schematic drawing showing an optical reflectance conversiondevice 4 included in a display apparatus 100, according to anembodiment. The optical reflectance conversion device 4 depicted in FIG.12 is a kind of electro-chromic device. However, the optical reflectanceconversion device 4 according present embodiments are not limited to theelectro-chromic device depicted in FIG. 12 and may be electro-chromicdevices having various structures.

Referring to FIG. 12, an aspect of the electro-chromic device is thatthe electro-chromic device includes a pair of transparent electrodelayers 111 and 112 to which a power is applied, and an electro-chromicmaterial layer 113 interposed between the pair of transparent electrodelayers 111 and 112.

The transparent electrode layers 111 and 112 may be formed of aconductive material of ITO, IZO, ZnO, and In₂O₃. Substrates 101 and 102may further be included on external sides of the transparent electrodelayers 111 and 112, respectively.

The electro-chromic material layer 113 includes an electro-chromicmaterial.

When an electrical current or a voltage is applied to theelectro-chromic material, the phase of the electro-chromic material ischanged whereby the optical reflectance of the display apparatus 100 iscontrolled. For example, the electro-chromic material may be one ofmagnesium (Mg), nickel (Ni), palladium (Pd), aluminum (Al), tantalumpentoxide (Ta₂O₅), hexagonal hydrogen tungsten bronze (HxWO₃), tungstenoxide (WO₃), and nickel oxide (NiOxHy).

When a predetermined power is applied to the transparent electrodelayers 111 and 112, the electro-chromic material of the electro-chromicdevice is changed from a transparent state to a mirror phase by reactingwith ions or electrons in an electrolyte. For example, in a state that afirst power is applied to the optical reflectance conversion device 4,the optical reflectance conversion device 4 is transparent. However, ina state that the second power is applied, the optical reflectanceconversion device 4 shows metal reflection characteristics like anopaque mirror, and when the third power is applied, the opticalreflectance conversion device 4 shows semitransparent mirrorcharacteristics. The magnitude of the power and the degree of changingthe reflectance of the optical reflectance conversion device 4 may bedetermined when a product is manufactured. The technology ofmanufacturing the optical reflectance conversion device 4 is well knownin the art.

The configuration of the electro-chromic device is not limited thereto,and a catalyst layer that includes Pd, a buffer layer that includes Al,and an electrolyte layer that facilitates ion conduction of theelectro-chromic material may further be formed as an additional layer114 on the electro-chromic material layer 113. These layers can increasethe electro-chromic efficiency or stabilize the electro-chromic device.

By way of summation and review, transparent display apparatuses have afixed transmittance. Therefore, the transmittance of the transparentdisplay apparatuses may not be controlled by a user, and may have areduced contrast ratio due to reflection of external light. Even thoughthe reflected light may be shielded by attaching an optical filter on afront surface of the transparent display apparatus, external light thatenters from a rear surface of the display apparatus through thetransparent region reduces the contrast ratio of the display apparatus.Therefore, there is a need to develop a display apparatus that canreduce the contrast ratio, and has transparency.

Embodiments are directed to a transparent display apparatus that canreduce the contrast ratio by disposing an optical filter and an opticalreflectance conversion device in each operation mode of the transparentdisplay device, and a method of operating the transparent displayapparatus.

Exemplary embodiments have been disclosed herein, and although specificterms are employed, they are used and are to be interpreted in a genericand descriptive sense only and not for purpose of limitation.

1. A display apparatus, comprising: a first substrate defined by a pixelregion and a transmitting region adjacent to the pixel region, the pixelregion emitting light in a first direction and the transmitting regiontransmitting external light; a second substrate that faces the firstsubstrate and seals pixels defined on the first substrate; an opticalfilter arranged on a first side of the display apparatus through whichlight is emitted, the optical filter being configured to transmitcircularly polarized light that rotates in a predetermined direction;and an optical reflectance conversion device arranged on a second sideof the display apparatus, opposite the first side, the opticalreflectance conversion device being configured to change a reflectanceof the external light according to modes of operation of the displayapparatus.
 2. The display apparatus as claimed in claim 1, wherein apixel of the pixels includes: a pixel circuit unit in the pixel regionon the first substrate, the pixel circuit unit including at least onethin-film transistor; a first insulating film covers at least the pixelcircuit unit; a first electrode on the first insulating film andelectrically connected to the pixel circuit unit, the first electrodelocated in the pixel region and not overlapping the pixel circuit unit,and the first electrode is formed of a transparent conductive material;a second electrode configured to reflect light emitted in a directiontowards the first electrode, the second electrode facing the firstelectrode and located in the pixel region; and an organic film betweenthe first electrode and the second electrode, the organic film includinga light-emitting layer.
 3. The display apparatus as claimed in claim 2,wherein the optical filter is on an outer side of the first substrateand the optical reflectance conversion device is on an outer side of thesecond substrate.
 4. The display apparatus as claimed in claim 2,wherein the pixel includes the transmitting region and a plurality ofthe pixel regions separated from each other by interposing thetransmitting region therebetween.
 5. The display apparatus as claimed inclaim 2, further comprising a second insulating film that does not coversome of the first electrode, the second insulating film located at leaston a pixel region portion of the pixel region and on the transmittingregion on the first insulating film, wherein the organic film is locatedon a first electrode portion of the first electrode that is not coveredby the second insulating film.
 6. The display apparatus as claimed inclaim 1, wherein a pixel of the pixels includes: a pixel circuit unitlocated in the pixel region on the first substrate, the pixel circuitunit including at least one thin-film transistor; a first insulatingfilm covers at least the pixel circuit unit; a first electrode on thefirst insulating film and electrically connected to the pixel circuitunit, the first electrode located in the pixel region and overlappingwith the pixel circuit unit, and the first electrode includes aconductive material reflection; a second electrode facing the firstelectrode and configured to reflect light to be emitted in a directionopposite to the first electrode; and an organic film between the firstelectrode and the second electrodes, the organic film including alight-emitting layer.
 7. The display apparatus as claimed in claim 6,wherein the optical filter is on an outer side of the second substrateand the optical reflectance conversion device is on an outer side of thefirst substrate.
 8. The display apparatus as claimed in claim 6, whereinthe pixel includes the transmitting region and a plurality of the pixelregions separated from each other by interposing the transmittingregion.
 9. The display apparatus as claimed in claim 6, furthercomprising a second insulating film that does not cover some of thefirst electrode, the second insulating film located at least on a pixelregion portion of the pixel region and on the transmitting region on thefirst insulating film, wherein the organic film is located on a firstelectrode portion of the first electrode that is not covered by thesecond insulating film.
 10. The display apparatus as claimed in claim 1,wherein the optical filter is a combination of a linear polarizingfilter and a Lamda/4 retarder or a circularly polarizing filter.
 11. Thedisplay apparatus as claimed in claim 1, wherein the optical reflectanceconversion device has a limitation that a sum of the reflectance of theexternal light and a transmittance of the external light is one.
 12. Thedisplay apparatus as claimed in claim 1, wherein the optical reflectanceconversion device is a liquid crystal device or an electro-chromicdevice.
 13. The display apparatus as claimed in claim 12, wherein theelectro-chromic device includes: a pair of transparent electrode layersto which power is applied; and an electro-chromic material layer betweenthe transparent electrode layers and including an electro-chromicmaterial, a phase of which is changed by a power applied to thetransparent electrode layers to control an optical reflectance of thedisplay apparatus.
 14. The display apparatus as claimed in claim 1,wherein, in a first mode, the optical reflectance conversion devicetransmits the external light that enters through the optical filter andthe display device.
 15. The display apparatus as claimed in claim 1,wherein, in a second mode, the optical reflectance conversion devicereflects the external light entering through the optical filter and thedisplay device.
 16. The display apparatus as claimed in claim 15,wherein, in the second mode, the external light that is reflected by theoptical reflectance conversion device is not re-transmitted through theoptical filter.
 17. The display apparatus as claimed in claim 1,wherein, in a third mode, the optical reflectance conversion devicereflects an external light portion of the external light enteringthrough the optical filter and the display device and transmits theother external light portion of the external light.
 18. The displayapparatus as claimed in claim 17, wherein, in the third mode, theexternal light portion of the external light that is reflected by theoptical reflectance conversion device is not re-transmitted through theoptical filter.
 19. A method of operating the display apparatus thatincludes a display device, an optical filter arranged on a first side ofthe display apparatus to which light is emitted, the optical filterbeing configured to transmit circularly polarized light that rotates ina predetermined direction, and an optical reflectance conversionarranged on a second side of the display apparatus, opposite the firstside, the optical reflectance conversion device being configured tochange a reflectance of the external light according to modes ofoperation of the display apparatus, the method comprising: realizing afirst mode, a second mode, and a third mode by controlling thereflectance of the external light that is transmitted through theoptical filter and the display device by applying different powers tothe optical reflectance conversion device.
 20. The method as claimed inclaim 19, wherein realizing the first mode includes: applying a firstpower to the optical reflectance conversion device; displaying an imagein the first direction in the display device; and transmitting theexternal light in a second direction, opposite the first direction,through the optical filter, the display device, and the opticalreflectance conversion device.
 21. (canceled)
 22. (canceled)